Pour the reserved stock into a bowl and let rest for 10 minutes. Skim fat and discard. Transfer stock to saucepan and add turkey neck, gizzard, and heart. Bring stock to a boil, reduce heat to low, cover, and boil gently for 1 hour. Remove the neck, gizzard, and heart, pick the meat from the neck, and chop the meat with gizzard and heart. Return to the stock and defat.